Willis Benson Machen (April 10, 1810 - September 29, 1893) was a Democratic U.S. Senator from Kentucky.
Born in Caldwell County, Kentucky (now Lyon County, Kentucky, Machen attended Cumberland College in Princeton, Kentucky, and then engaged in agricultural pursuits near Eddyville, Kentucky. He was delegate to the State constitutional convention in 1849, was a member of the Kentucky Senate in 1854, and was a member of the Kentucky House of Representatives in 1856 and 1860. He was also elected to the First and Second Confederate Congresses.
Machen was appointed as a Democrat to the United States Senate to fill the vacancy caused by the death of Garrett Davis, and served from September 27, 1872 to March 3, 1873, after which he resumed agricultural interests. He died in Hopkinsville, Kentucky, and was intered in Riverview Cemetery, Eddyville.
Preceded by: Garrett Davis United States Senator (Class 3) from Kentucky 1872-1873 Succeeded by: Thomas C. McCreery